Method of making spark plug unit bushings



Dec. 11,1945. 'r. N. WILLCOX 2,390,821

METHOD OF MAKING SPARK PLUG UNIT BUSHINGS Filed 001;. 11, 1943 I nventor: Thomas N. Willcox -i-lis Attorney.

Patented Dec. 11, 1945 METHOD OF MAKING SPARK PLU UNIT BUSHINGS Thomas N. Willcox, Pittsficld, Mass., assignor to General Electric Company, a corporation of New York ApplicationOctober 11, 1943, Serial No. 505,731

Claims.

My invention relates to an improved method of making a bushing for a spark plug unit.

In molding bushings of resilient insulating material to provide a resilient lining within a relatively rigid insulating boot of a frangible material such as a ceramic or a boro-silicate-mica composition, considerable difficulty has been experienced due to the cracking of the boot during the molding operation. I have found that this cracking can be prevented by molding the resilient insulating material under pressure about substantially all surfaces of the boot, such that all parts of the boot are subjected to substantially the same temperature and pressure.

An object of my invention is to provide an im proved method of making a bushing for a spark plug unit in which a resilient sleeve is intimately bonded to the inner surface of a relatively rigid insulating boot. I

Another object of my invention is to provide an improved method of molding resilient insulating material under pressure about a relatively rigid insulating boot.

Further objects and advantages of my invention will become apparent and my invention will be better understood from the following description referring to the accompanying drawing and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In the drawing, Fig. 1 is a plan view, partly broken away, showing a mold used in my improved process and a bushing made by this process; Fig. 2 is an enlarged view of the bushing made in the mold shown in Fig. 1 illustrating this bushing after it has been removed from the mold and before finishing; and Fig. 3 is a partial sectional view of the bushing shown in Figs. 1 and 2 in its finished condition.

Referring to the drawing, I have shown a method of carrying out my invention which includes making a bushing for a spark plug unit by forming a relatively rigid tubular insulating material boot ID with an adhesively roughened or otherwise treated inner surface I l which extends from one ,end H to an inwardly extending fiange l3 near the opposite .end of theboot. 'This surface may be treated in. any suitable manner, as by etching 'it with dilute 4% hydrochloric acid at room temperature, abrading this surface with a file, said blasting this surface, carefully washing this surface with wetting agents, such as a 1 solution of Aerosol or a 5% solution of Naconol, or by coating this surface with a suitable cement, such as a synthetic rubber cement and using it either baked or unbaked to provide a surface to which a resilient insulating material, such as a synthetic rubber, will become intimately bonded when molded under heat and pressure.

The boot I0 is then arranged in a mold M which is formed to provide a molding space about substantially all surfaces of. the boot except for a relatively small supporting portion l5 which is adapted to hold the boot in position during the molding operation. The mold also is formed with a supporting groove into which a ring It of electrically conductive material is placed and about w hich a collar can be molded of the resilient insulating material which will extend about the end 52 of the boot I3 and be integrally connected with a sleeve portion ll of the resilient material which may be molded in a tubular molding spacev extending through substantially the full length of the boot. The mold also is formed witha tubular section extending from the collar space away from the boot into which an axially extending sleeve portion I8 may be formed. As shown in Fig. l, a tubular molding space also is formed about the outside of the boot 10 into which a sleeve of insulating material I9 is adapted to be molded.

In carrying out the molding operation, a fluid resilient and yi'eldable insulating material is molded under heat and pressure into the above-' described molding spaces through two pairs of gates 20 and H in the mold which feed the resilient insulating material under pressure into the molding spaces and about. substantially all sides of the boot l0, and the air within the mold is allowed to escape through slight clearances around the molding pins 22 and 23 in the ends of the mold l4. After this molding operation, the bushing is removed from the mold and is in the form shown in Fig. 2 with'a pair of ears 24 extendingfrom the sleeve portion l8 and with 'a pair of ears 25 extending from the sleeve l9 which extends over the outside of the boot Ill; The ears 24 are then removed from the sleeve portion I8 and the molded insulating material forming the outside sleeve i9 is removed from the outside of the boot in any suitable manner, as by peeling it off as shown in Fig. 2, and from about the end of the boot away from a collar 26 formed over the end I2 of the boot I'll. This forms a unitary bushing including the boot III of relatively rigid material such as a ceramic or boro-silicate-mica,

provided with a lining I! of resilient material which is intimately bonded to substantially the entire inner surface of the boot III, as shown in Fig. 3. This bushingconstruction is the joint invention of Hubert H. Race and the applicant and forms the subject matter of patent application, Serial No. 505,730, filed October 11, 1943, and is assigned to the same assignee as this application.

While I have illustrated and described a particular embodiment of my invention, modification thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular method disclosed, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my inven tion.

What I claim as new and desire to secure by Letters Patent of the United States is:

tion extending from the collar away from the boot and to provide an intimately bonded connection between the inner boot surface and the engaging surface of the resilient material sleeve, and removing the molded resilient material from the outside of the boot and from the end of the boot away from the molded collar.

6. The method of making a spark plug unit bushing which includes forming a relatively rigid tubular insulating boot of frangible material with a treated inner surface, molding a resilient and yieldable insulating material sleeve under pressure around substantially all surfaces of the boot except a small supporting portion for preventing 1. The method of making a bushing which includes forming a relatively rigid tubular insulating boot of frangible material, molding a resilient insulating material sleeve under pressure about substantially all surfaces of the boot for preventing cracking of the boot during said molding and to provide a sleeve extending through substantially the full length of the boot, and removing the molded resilient material from the outside of the boot.

2. The method of making a bushing which includes forming a relatively rigid tubular boot of frangible material with a roughened inner surface, molding a resilient material sleeve about substantially all surfaces of the boot for preventing cracking of the boot during said molding and to provide a sleeve extending through substantially the full length of the boot having an intimately bonded connection with the inner boot surface, and removing the molded resilient material from the outside of theboot.

3. The method of making a spark plug unit bushing which includes forming a relatively rigid tubular insulating boot of frangible material with an adhesively treated inner surface, molding a resilient insulating material sleeve under pressure about substantially all surfaces of the boot for preventing cracking of the boot during said molding and to provide an intimately bonded connection between the inner boot surface and the engaging surface of the resilient material sleeve, and removing the molded resilient material from the outside of the boot.

4. The method of making a bushing which includes forming a relatively rigid tubular boot of frangible material with a roughened inner surface, molding a resilient material sleeve under pressure about substantially all surfaces-of the boot for preventing cracking of the boot during said molding and to provide a sleeve extending through substantially the full length of the boot with a molded collar extending over one end of the boot and having an intimately bonded connection between the inner boot surface and the engaging surface of the resilient material sleeve,

and removing the molded resilient material from the outside of the boot and from the end of the boot away from the molded collar.

5. The method of making a bushing which includes forming a relatively rigid tubular insulating boot of frangible material with an adhesively treated inner surface, molding a resilient insulating material sleeve under pressure about substantially all surfaces of the boot for preventing cracking of the boot during said molding and to provide a sleeve with a molded collarextending over one end of-the boot and a tubular seccracking of the boot during said molding and to provide a sleeve extending through substantially the full length of the boot with a molded collar extending over one end of the boot and a tubular section extending from the collar away from theboot to provide an intimately bonded connection between the inner boot surface and the engaging surface of the resilient material sleeve, and removing the molded resilient material from the outside of the boot and from the end of the boot away from the molded collar.

7. The method of making a spark plug unit bushing which includes forming a relatively rigid tubular insulating boot of frangible material with an adhesively treated inner surface, arranging this boot in mold formed to provide a molding space about substantially all surfaces of the boot except a small supporting portion, molding a resilient and yieldable insulating material sleeve under pressure into the molding space to provide an intimately bonded connection between the inner boot surface and the engaging surface of the resilient material sleeve, removing the bushing from the mold, and removing the molded resilient material from the outside of the boot.

8. The method of making a spark plug unit bushing which includes forming a relatively rigid tubular insulating boot of frangible material with a treated inner surface, arranging this boot in a mold formed to provide a molding space about substantially all surfaces of the boot to provide a tubular molding space extending through substantially the full length of the boot with a space removing the molded resilient material from the outside of the boot and from the end of the boot away from the molded collar.

9. The method of making a spark plug unit bushing which includes forming a relatively rigid tubular insulating boot of frangible material with a roughened inner surface, arranging this boot in a mold formed to provide a molding space about substantially all surfaces of the boot except a, small supporting portion to provide a tubular molding space extending through substantially the full length of the boot with a space for molding a collar extending over one end of the boot, molding a resilient insulating material sleeve under ressure into the molding spaces to provide an intimately bonded connection between the roughened inner boot surface and the engaging surface of the resilient material sleeve, removing the bushing from the mold, and removing the molded resilient material from the outthe boot and a tubular section extending from the collar space away from the boot, molding a resilient and yieldable insulating material sleeve under pressure into the molding spaces to provide an intimately bonded connection between the roughened inner boot surface and the engaging surface of the resilient material sleeve, removing the bushing from the mold; and removing the molded resilient material from the outside of the boot and from the end of the boot away from the molded collar section.

- THOMAS N. WILLCOX. 

